Electrical resistance heating articles



Dec. 17, 1968 Filed Oct. 14, 1965 2 Sheets-Sheet 1 L -11. W I U U" MW L FIG?) lm liilihl JJJMM JJ GEORGE J. SHOMPHE ROBERT W. TABOR HAROLD W. LALMOND r EMILE ImuJLIJLIILIHIJLIHIJ' FIG. 2.

BY Wddfi. him

ATTORNEY Dec. 17, 1968 G. J. SHOMPHE ET AL 3,417,229

ELECTRICAL RESISTANCE HEATING ARTICLES Filed Oct. 14, 1965 2 Sheets-Sheet z 6 INVENTORS GEORGE J. SHOMPHE ROBERT W. TABOR HAROLD W. LALMOND BY ATTORNEY United States Patent 3,417,229 ELECTRICAL RESISTANCE HEATING ARTICLES George J. Shomphe, Robert W. Tabor, and Harold W.

Lalmond, Nashua, N.H., assignors to Sanders Associates, Inc., Nashua, N.H., a corporation of Delaware Filed Oct. 14, 1965, Ser. No. 496,021 8 Claims. (Cl. 219-528) ABSTRACT OF THE DISCLOSURE Articles which provide uniform emission of heat from the surfaces thereof utilizing thin, flexible resistive strips as heating elements. The element strips are encapsulated within electrical, flame-retardant flexible material which may be covered with decorative type materials. The heat ing circuit having a plurality of heating elements connected in parallel between a power bus and a ground bus. Each heating element has a thermal-link fuse as an integral part thereof and a detachment of one element will not aflFect the operation of the other elements.

This invention relates to flat, flexible, electrical heating elements and to the use of such heating elements in combination with and as integral parts of heating pads, electric blankets, decorative wall heating panels and the like.

State-of-the-art articles of the type comprehended by this invention generally utilize asbestos wrapped heater wires which are strung back and forth through padded materials. Such articles include blankets, heating pads, etc. The electrical heating of homes and oflices is commonly achieved by means of resistive heating elements which are embedded in insulation panels and inserted into or behind building Walls. Alternatively, radiant heating cable is installed within either plaster or dry wall ceilings or embedded in concrete slab floors.

There are many deficiencies which render such currently available articles undesirable. It is toward the correction of these deficiencies that the present invention is directed. A common problem, for instance, is that although the asbestos covering and electrical insulation of heater wires and elements meets National Fire Underwriter specifications at the time of purchase, subsequent use may cause the asbestos binding to become loose or break. The asbestos may then unravel and expose the heater element, thus enhancing the danger of electrical shock or fire. Another problem with currently available electrical resistance heating articles is that the coiled wire heating elements are relatively inflexible and cause lumps in heating pads, electrical blankets, etc., resulting in appreciable discomfort to the user. Also, because of the size and geometry of conventional heater element wires, relatively large spacing is required between adjacent turns. This results in uneven heat emission from the article. Finally, all prior art heating pads, blankets, and the like are assemblies of various elements. The preparation and assembly of the various separate elements results in higher costs of the articles.

Accordingly, it is a principal object of this invention to provide a new and improved heating element for use in heating pads, electrical resistance heating wall panels, electrical blankets, and the like.

It is another object of this invention to provide a new and improved insulated electrical resistance heating element that is smooth, thin and flexible, and has particular utility in combination with decorative type materials in the fabrication of articles such as heated upholstery, wall coverings, ceiling coverings, foot pads, articles of clothing and the like.

It is another object of this invention to provide articles of the type described wherein the heater element is encapsulated within electrical and flame-retardant material suitable to eliminate the possibility of exposed heating wires.

It is another object of this invention to provide articles of the type described having insulation material adapted to protect the heater element from exposure, penetration of moisture and the like.

It is another object of this invention to provide articles of the type described having a heater element of flat, thin strips of resistive material that is highly flexible and causes no lumps or stiffness in the finished article.

It is another object of this invention to provide articles of the type described having a heating element of closely spaced, thin, flat strips of resistive material adapted to produce a uniform emission of heat from the articles surface.

It is another object of this invention to provide electrical resistance wall panel heating means having the appearance, flexibility, and ease of installation of conventional wall covering.

It is another object of this invention to provide electrical resistance wall panel heating means having a multiplicity of discrete heating units which may be selectively detached or severed without affecting the heating capacity of the remaining panel.

It is another object of this invention to provide electrical resistance wall panel heating means having a novel thermal fuse as an integral part of each heater element.

These, together with other objects and features of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which like elements are given like reference numerals throughout, and wherem:

FIGURE 1 is an orthogonal, partially exploded view of the wall panel embodiment of the invention;

FIGURE 2 is a detail of the wall panel of FIG. 1 having the outer layers of decorative coating and insulation removed;

FIGURE 3 is a detail of the Wall panel of FIG. 1 illustrating a longitudinal section thereof;

FIGURE 4 illustrates the electrical connections and panel arrangement of a wall covered with the panel material of FIG. 1;

FIGURE 5 is a detail of the panel material of FIG. 1 showing the novel thermal fuse element of the present invention; and

FIGURE 6 is a sectional view of FIG. 5 taken at 66.

The most significant feature of the invention and one that is common to all embodiments and applications is a unique flexible ins illation-encapsulated heating element. This heating element has all of the desirable characteristics of flexible printed circuits of the type disclosed in the patent application of Victor F. Dahlgren, Serial No. 2,997,521 and assigned to the assignee of the present invention. That is, a thin, flat, electrical circuit is laminated between sheets of flexible plastic material, thus providing thin, smooth, large-area sheets which contain a given electrical circuit. The present invention, however, differs in that the conductive copper sheets which are used for the electrical circuits of Dahlgren are replaced by thin sheets of flexible steel or other suitable resistive material.

After lamination to one of the plastic sheets, the thin steel sheets are etched to provide the desired heater pattern. The exact nature of the materials comprehended by the invention will be described with reference to particular figures of the drawings.

The flat, flexible heating unit of the present invention overcomes many of the undesirable characteristics of prior art articles which employ electrical resistance heating means. It is intended that the heating element of the present invention be used in combination with a great variety of covering materials and for a great variety of applications. For instance, heating pads may be fabri cated by covering the heating element with conventional cloth or any of a great many fabrics. A particularly desirable combination for a heating pad comprises the heating element of the present invention having a covering of heat-expandable plastic. Such a heating pad is flexible, safe and comfortably padded. It is also intended that the heating element be covered with washable vinyls to provide articles which may be readily washed without effecting the electrical characteristics of the heating circuit. The flat, flexible heating element of the present invention is also particularly adaptable for heated upholstery whereby therapeutic furniture and commercial applications such as bus and airline seats are made feasible and economical. Other similar applications such as heated "blankets, heated articles of clothing such as heated gloves and foot pads as well as covers for food warmers, batteries and the like are obvious extensions of the subject invention.

Perhaps the most significant application of the invention relates to electrical resistance heating of homes and offices. It is comprehended that the present invention, together with the various features and combinations thereof to be hereinafter described, should be used as integral parts of a wall panel electrical resistanpc heating system. Such a wall panel electrical resistance heating system essentially takes the form of conventional wall coverings such as wallpaper, plastic wall covering and the like, and may be installed with similar ease. Inasmuch as the wall cover embodiment of the present invention incorporates substantially all of the features of the invention, the ensuing detailed descriptions will particularly reference such embodiment. There is, of course, no intention to so limit the invention, the description of this particular embodiment being by way of example only.

Referring now to FIGS. 1, 2, 3 and 4, there is illustrated in detail the wall covering embodiment of the invention. FIG. 1 is a partially exploded orthogonal view which illustrates the various components of such a heating panel. That is, the heater circuit 1 is laminated between layers of insulating material 2 and 3 and a decorative covering 5 is attached to the outer surface of insulating material 3. A heat-reflecting sheet 4 may be applied to the outer surface of insulating material 2 if desired. Such a heat reflecting means may comprise silver paint, polished metal foil, aluminum foil, or any appropriate material which will reflect the heat radiated by electrical resistance heating circuit 1. Since the installation of wall covering having such a reflective backing may require a special adhesive, a paper backing may be included on the wall covering at the time of fabrication. That is, the paper backing is applied by the special adhesive, thus providing a finished product which may be installed with conventional adhesive.

FIGS. 2 and 3 illustrate in considerable detail the heating circuit 1, including the power and ground busses and the presently preferred heater element arrangement. In particular, FIG. 2 illustrates one section of a panel such as illustrated in FIG. 1 having the decorative coating and first insulation layer removed. A ground bus 6 is provided which runs along each edge of the bottom layer of insulating material 2, and an electrical power bus 7 is provided to run between and parellel to the ground busses as shown. Finally, a plurality of electrical resistance heating elements or units 8 are provided in parallel between electrical power bus 7 and ground busses 6. Ground busses 6, and electrical power bus 7, may be of conductive material such as copper or they may be fabricated of the same resistive material as heater units 8. They should, however, be of greater width to preclude excessive voltage drop in the vertical feed bus. It is apparent from this arrangement that any heater unit 8 may be removed or severed from the panel without affecting the circuit conheater units, provided that the feeder bus connection is maintained. This particular feature of the invention greatly facilitates the installation of panels into homes where considerable cutting is required to make the wall covering conform with the room dimensions. It is also pointed out that the particular configuration of each heating unit 8 is such that maximum uniformity of heat radiation is provided. That is, the continuous heating strip of each unit is of relatively wide and very thin dimensions which permit a closely spaced parallel configuration. This unitary severable construction, together with the feature'of uniform heat emission, is of course a particularly desirable characteristic of all embodiments of the invention.

It is not intended that the invention be limited to the particular'exemplary configuration illustrated in the drawings. An obvious extension of the novel concepts disclosed herein is that of a plurality of interlaced circuits that can be selectively switched on and off and are suitable to establish and maintain various temperature levels. This may also be accomplished by selective grouping of the heater elements shown in the drawings into a plurality of discrete circuits.

Layers of insulating material 2 and 3 are preferably of a dielectric material that is flame-retardant. There are many thermplastic materails such as polychlorotrifluoroethylene, fluorinated ethylene propylene copolymer, and

polyimide fluorinated ethylene propylene, which are suitable for=this purpose and which provide adequate electrical insulation. One presently preferred material is polyvinyl chloride acetate copolymer. To this is added a flame-retardant constituent such as antimony tri-oxide.

The heater circuit 1 may be fabricated in any conventional manner. However, printed circuit techniques are generally preferred. By way of example, an electrical resistance heating panel as illustrated in FIG. 1 may be fabricated in accordance with the following steps:

(1) A .002 inch thick steel foil sheet is pumiced and degreased.

(2) A coating of rubber based adhesive such as that sold by Conap Corporation under the trade name Conap Primer 1131 is applied to each surface thereof.

(3) The foil is oven-dried for 15 minutes at an elevated temperature of approximately 200 F.

(4) The sheet of steel is laminated to a sheet of 10-mil vinyl such as the polyvinyl chloride acetate copolymer referred to above.

(5) The vinyl and steel foil are brought to 160 C.

(6) The vinyl and steel foil are compressed at a pressure of 32.4 pounds per square inch.

(7) The work is cycled 12 minutes.

(8) The desired circuit is screened onto the steel foil using acid resist ink.

(9) The steel foil is then etched in accordance with printed circuit techniques.

(10) The surface is then washed in naphtha.

(11) The cover coat of vinyl is then applied, using the same procedure outlined in steps 1 through 9.

(12) Excess plastic is trimmed from the panel.

(13) The vinyl is stripped from the termination points and the line supply cord is soldered thereto.

FIG. 4 illustrates a wall having a plurality of panels of the type illustrated by FIG. 1 installed thereon. The installation as illustrated in FIG. 4 includes a ground bus 9, which connects all ground busses 6 of the various panels. A -volt house supply 11 is stepped down to 24 volts at each panel by transformers 10. In this manner the panels are energized by 24 volts and thus conform to National Safety Conference Code standards. It is of course also possible to provide a single transformer which will deliver 24 volts to all of the panels used in any given room. Such a transformer, however, would require exceptionally heavy connecting leads for the cumulative current required. It is another feature of the invention,

however, to include on each panel a printed circuit bi-filar type transformer 14 (schematically illustrated in FIG. 2). Such a printed circuit transformer may be fabricated as part of the heating panel in accordance with conventional printed circuit techniques.

It is another feature of the invention to provide a unique thermal fuse as an integral part of each heater unit. Such a unique thermal fuse is illustrated by FIGS. 5 and 6 and preferably is inserted into the circuit of each individual heater unit 8. The thermal fuse comprises a fusible metal alloy link 13 in the heater element circuit. A pocket 12 is provided in the layers of insulating material 2 and 3 to accommodate the fusible link. Although this fusible link may be designed to fuse at any desired temperature by the proper selection of materials, it is currently preferred that a link of 48% tin and 52% indium be used. A 50% tin, 50% indium link also has been found to be suitable for most applications. Such a link fuses at approximately 117 C. It is also intended that a coagulating element (that is, an element effective to cause the melted alloy to ball up) be added to the fusible link to insure a complete break in the electrical circuit when the critical temperature is reached or exceeded. A coating of any resinous material is suitable for this purpose.

Temperature controls for the above-described articles are also comprehended by the invention. Such controls may be conventional commercially available devices and may be located in any appropriate place.

There have thus been disclosed apparatus and articles suitable to accomplish the various stated objects of the invention. It is to be understood that the above description with reference to particular embodiments of the invention was by way of example only and that there is no intention to limit the invention to such specific embodiments. The true spirit and scope of the invention, therefore, is to be limited only by the following claims.

What is claimed is:

1. A decorative electrical resistance heating panel comprising first and second strips of flame-retardant electrical insulation, a thin, flat electrical printed circuit including a plurality of discrete resistance heating elements disposed therebetween, said electrical circuit comprising a centrally disposed strip power bus, first and second strip ground bosses in juxtaposition therewith disposed proximate the outer edge of said panel, a plurality of resistance heating elements connected in parallel between said power bus and each said strip ground bus, and a decorative covering on the outer surface of one of said strips of insulation.

2. A heating panel as defined in claim 1 including a heat-reflecting means covering the surface of said panel opposite to said decorative covering.

3. A heating panel as defined in claim 1 including a thermal fuse in each said electrical resistance heating element.

4. A heating panel as defined in claim 3 where each said thermal fuse comprises a heat-fusible link in bridging relationship with a severed portion of each said discrete resistance heating element.

5. A heating panel as defined in clai-m 4 wherein said heat-fusible link comprises an alloy of 48% tin and 52% indium.

6. A heating panel as defined in claim 5 wherein each said heat-fusible link is provided with a coating of resinous material.

7. A heating panel as defined in claim 1 including a printed circuit transformer operatively connected to said electrical circuit and being adapted to reduce the supply voltage to less than 30 volts.

8. A decorative electrical resistance heating panel comprising first and second strips of flexible electrical insulation, a thin, flat electrical printed circuit disposed therebetween, the electrical printed circuit comprising a centrally disposed strip power bus, first and second strip ground busses disposed proximate the outer edges of said panel, and a plurality of resistance heating elements connected in parallel between said power bus and each said strip ground bus; a printed circuit transformer operatively connected to said electrical circuit, and a decorative covering on the outer surface of One of said strips of insulation.

References Cited UNITED STATES PATENTS 888,381 5/1908 Andrews et al. 219-517X 1,549,984 8/1925 Hynes 219-517 X 1,979,082 10/1934 Schwedenberg et al. 219-582 X 2,314,766 3/1943 Bull et al. 219-213 2,712,591 7/1955 Rogell 219-528 X 2,719,213 9/1955 Johnson 338-2 .1 2,782,289 2/ 1957 Nathanson 219-528 3,221,145 11/ 1965 Hager 219-549 3,263,307 8/1966 Lund et al. 29-1555 2,600,486 6/1952 Cox 338-212 2,613,306 10/1952 Waltersdorf et al. 338-212 X 2,641,675 6/1953 Hannahs 174-685 2,745,942 5/1956 Cohen 219-528 2,873,352 2/1959 Franco 219-528 3,283,284 11/1966 Eisler 338-212 2,703,352 3/1955 Kozacka 200- X FOREIGN PATENTS 713,684 8/1954 Great Britain.

765,709 1/ 7 Great Britain.

BERNARD L. GILHEANY, Primary Examiner. VOLODYMYR Y. MAYEWSKY, Assistant Examiner.

U.S. Cl. X.R. 

